/* Down or "P" operation on a semaphore. Waits for SEMA's value
* to become positive and then atomically decrements it.
*
* This function may sleep, so it must not be called within an
* interrupt handler. This function may be called with
* interrupts disabled, but if it sleeps then the next scheduled
* thread will probably turn interrupts back on. */
void sema_down(struct semaphore *sema) {
enum intr_level old_level;
ASSERT(sema != NULL);
ASSERT(!intr_context());
old_level = intr_disable();
while (sema -> value == 0) {
/*
* 注释掉原有的代码
* list_push_back(&sema -> waiters, &thread_current() -> elem);
* thread_block();
*/
if (!thread_mlfqs) {
donate_priority();
}
list_insert_ordered(
&sema -> waiters,
&thread_current() -> elem,
(list_less_func *) &cmp_priority,
NULL
);
thread_block();
}
sema -> value--;
intr_set_level(old_level);
}
void donate_priority(struct thread *thread_, int priority){
thread_->priority=priority;
if(thread_->waiting_lock){
donate_priority(thread_->waiting_lock->holder, priority);
}
}
void donate_priority(struct thread *thread_, int priority){
thread_->priority=priority;
if(nested_priority > 7)
return;
if(thread_->waiting_lock){
if(thread_->waiting_lock->holder->priority < priority){
nested_priority++;
donate_priority(thread_->waiting_lock->holder, priority);
}
}
}
// Refresh donated priorities of all the threads dependent on current threads.
void refresh_donated_priority_down (struct thread* acquirer) {
int i;
for (i=0; i < lock_list_cnt; i++) {
struct list_elem* e;
struct list* waiter_list = &lock_list[i]->semaphore.waiters;
for (e = &waiter_list->head; e != list_end(waiter_list); e = e->next) {
if (list_entry(e, struct thread, elem) == acquirer) {
if (lock_list[i]->holder->effective_priority < acquirer->effective_priority)
donate_priority(lock_list[i]->holder, acquirer->effective_priority);
refresh_donated_priority_down (lock_list[i]->holder);
break;
}
}
}
}
void lock_sema_up (struct semaphore *sema, struct thread* holder) {
ASSERT (!thread_mlfqs);
enum intr_level old_level;
ASSERT (sema != NULL);
old_level = intr_disable ();
if (!list_empty (&sema->waiters)) {
// P2: find out thread with highest priority.
struct list_elem* max_elem = list_max(&sema->waiters, priority_less, NULL);
list_remove (max_elem);
// P2: calculate and assign donate priority.
donate_priority (holder, calculate_donated_priority_up(holder));
thread_unblock (list_entry (max_elem, struct thread, elem));
}
sema->value++;
intr_set_level (old_level);
thread_yield(); // p2
}
